Re: [CAD_CAM_EDM_DRO] Looks Like tonight is the night for questions

Doug Harrison wrote:

> Hi Art;
>
> How fast your motor will run is one of those "yer on yer own" things. I
> once asked a Baldor engineer at a trade show this same question with regard
> to his vector drive system. He said Baldor vector drive motors are rated
> for 5500 rpm. I asked where such information was published in their
> literature. I think his next comment was about the free hot wings being
> offered by the Hooters girls across the room. You get the picture.
>
> The tech guy at YCI Supermax told me I could easily run the 1740 rpm motor
> on my knee mill at 4000 rpm. I inquired who was doing this, to which he
> replied "lots of people." I've yet to try it.

If you look at the construction of 1140, 1740 and 3420 RPM motor rotors, you
won't find much difference. There may be some changes in the integral fan,
so the higher speed motors won't waste excessive power churning air
around. Otherwise, I don't think they make much of an adjustment for
safety factor in the lower integral-horsepower motors. 5500 RPM doesn't
sound too hairy. (Funny thing, 5500 is a standard speed for 8-pole 400 Hz
motors. I wonder where he pulled that number out of the air - maybe they
use standard rotors in 400 cycle 8-pole motors!)

I wouldn't get very worried running a 1740 RPM motor at 2x speed, ie. 120 Hz.
4000 RPM isn't much over that. It will increase vibration and shorten bearing

and belt life. Now, if you ran the motor up to 4000 RPM on the highest speed
setting, you'd get a spindle RPM something like 7000 RPM on the spindle, at
least the way a Bridgeport 1J head is set up. I don't know what that will do
to
your spindle bearings, which cost a LOT more than the motor bearings. But,
it has to shorten their life at least linearly, and may do worse than that.

Jon